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This research was carried out over a period of 60 days in the summer and autumn of 2005 in the Caspian Sea Aquaculture Research Station (Inland Water Aquaculture Research Center). Fingerlings of Rutilus frisii kutum weighting one gram were transferred to fiberglass 100 liter tanks each stocked with 35 fish. The fish were divided into five groups and treated with five treatments and three replicates including, fresh water, 4ppt, 6ppt, 8ppt, and 10ppt salinity by completely randomized design. We found that different salinities did not affect the mortality rate of the fish. Comparison of food conversion ratio (FCR), special growth rate (SGR) and weight gain (WG) between control and other treatments revealed a significant difference (p£0.05). We also found that the 4ppt treatment differed meaningfully with 8ppt and 10ppt treatments in terms of FCR, SGR and WG (p£0.05) and the same was true between 6ppt and 8ppt and 10ppt treatments for the FCR, SGR and WG. The results showed that the maximum and minimum weight gain were related to 10ppt treatment (mean 58.9±2.71) and control (mean 39.1±4.73) respectively. The minimum special growth rate (0.549±0.057) was referred to the control treatment and the maximum (0.772±0.028) was seen in 10ppt salinity. The minimum average FCR (3.93±0.122) was seen in 10ppt salinity and the maximum (5.6±0.601) was observed in the control treatment. According to the results, it is suggested that the optimal salinity for fingerlings with mean weight 1gr is 8ppt and 10ppt.

Caspian sand goby, Neogobius jluviatilis pallasi belongs to Gobiidae family. Because of their abundance in Caspian Sea, they have important role in the sea food chain in this area. This study was conducted from October 2005 to September 2006 in southwest coasts of the Caspian Sea in Guilan province. Samples were collected monthly from four stations (Astara, Anzali, Chamkhaleh and Chaboksar coasts) from coastal areas to waters 15meters deep using bottom trawl. Result of differential function analyses on corrected morphometric statistic showed three functions 51.3%, 28.4% and 20.3%, respectively, and sum of differentiative function percentage was 80% which proved difference among groups. The functions showed that samples in Astara station were completely different from other regions while they were similar to Anzali station only in some sampling points. Chamkhaleh and Astara stations were the same but Chaboksar station was a separated group. Analysis of differential functions for studied characteristics included on average 86.3% of the population with most of it belonging to Astara station (93.3%) and Anzali (90%). The minimum amount belonged to Chamkhaleh with 79.3%. The results showed that Neogobiusjluviatilis pallasi probably has three different populations in Astara, Anzali, Chamkhaleh and Chaboksar populations.